Cache for NtfsFileSystem.UsedSpace

* Significantly reduces delays when mounting as virtual file system.

Author: LTRData

Library/DiscUtils.Ntfs/ClusterBitmap.cs

@@ -20,12 +20,13 @@
 // DEALINGS IN THE SOFTWARE.
 //
 
+using DiscUtils.Streams;
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
-using DiscUtils.Streams;
 
 namespace DiscUtils.Ntfs;
 
@@ -36,6 +37,8 @@ internal class ClusterBitmap : IDisposable
 
     private long _nextDataCluster;
 
+    private long? _usedClusters;
+
     public ClusterBitmap(File file)
     {
         _file = file;
@@ -47,6 +50,35 @@ public ClusterBitmap(File file)
 
     internal Bitmap Bitmap { get; private set; }
 
+    public long GetUsedClustersCount()
+    {
+        if (_usedClusters is null)
+        {
+            long usedClusters = 0;
+            long processed = 0;
+
+            var bufferSize = (int)Math.Min(4 * Sizes.OneMiB, Bitmap.Size);
+            var buffer = ArrayPool<byte>.Shared.Rent(bufferSize);
+            try
+            {
+                while (processed < Bitmap.Size)
+                {
+                    var count = Bitmap.GetBytes(processed, buffer, 0, bufferSize);
+                    usedClusters += BitCounter.Count(buffer, 0, count);
+                    processed += count;
+                }
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
+
+            _usedClusters = usedClusters;
+        }
+
+        return _usedClusters.Value;
+    }
+
     public void Dispose()
     {
         if (Bitmap != null)
@@ -142,6 +174,8 @@ public List<Range<long, long>> AllocateClusters(long count, long proposedStart,
             _fragmentedDiskMode = numFound / result.Count < 4;
         }
 
+        _usedClusters += total;
+
         return result;
     }
 
@@ -232,19 +266,25 @@ public async ValueTask<List<Range<long, long>>> AllocateClustersAsync(long count
             _fragmentedDiskMode = numFound / result.Count < 4;
         }
 
+        _usedClusters += total;
+
         return result;
     }
 
     internal void MarkAllocated(long first, long count)
     {
         Bitmap.MarkPresentRange(first, count);
+
+        _usedClusters += count;
     }
 
     internal void FreeClusters(IEnumerable<Range<long, long>> runs)
     {
         foreach (var run in runs)
         {
             Bitmap.MarkAbsentRange(run.Offset, run.Count);
+
+            _usedClusters -= run.Count;
         }
     }
 
@@ -253,17 +293,23 @@ internal async ValueTask FreeClustersAsync(IEnumerable<Range<long, long>> runs,
         foreach (var run in runs)
         {
             await Bitmap.MarkAbsentRangeAsync(run.Offset, run.Count, cancellationToken).ConfigureAwait(false);
+
+            _usedClusters -= run.Count;
         }
     }
 
     internal void FreeClusters(Range<long, long> run)
     {
         Bitmap.MarkAbsentRange(run.Offset, run.Count);
+
+        _usedClusters -= run.Count;
     }
 
-    internal ValueTask FreeClustersAsync(Range<long, long> run, CancellationToken cancellationToken)
+    internal async ValueTask FreeClustersAsync(Range<long, long> run, CancellationToken cancellationToken)
     {
-        return Bitmap.MarkAbsentRangeAsync(run.Offset, run.Count, cancellationToken);
+        await Bitmap.MarkAbsentRangeAsync(run.Offset, run.Count, cancellationToken).ConfigureAwait(false);
+
+        _usedClusters -= run.Count;
     }
 
     /// <summary>
@@ -278,6 +324,8 @@ internal void SetTotalClusters(long numClusters)
         var actualClusters = Bitmap.SetTotalEntries(numClusters);
         if (actualClusters != numClusters)
         {
+            _usedClusters = null;
+
             MarkAllocated(numClusters, actualClusters - numClusters);
         }
     }
@@ -295,6 +343,9 @@ private long ExtendRun(long count, List<Range<long, long>> result, long start, l
         if (numFound > 0)
         {
             Bitmap.MarkPresentRange(start, numFound);
+
+            _usedClusters += numFound;
+
             result.Add(new Range<long, long>(start, numFound));
         }
 
@@ -314,6 +365,9 @@ private async ValueTask<long> ExtendRunAsync(long count, List<Range<long, long>>
         if (numFound > 0)
         {
             await Bitmap.MarkPresentRangeAsync(start, numFound, cancellationToken).ConfigureAwait(false);
+
+            _usedClusters += numFound;
+
             result.Add(new Range<long, long>(start, numFound));
         }
 

Library/DiscUtils.Ntfs/NtfsFileSystem.cs

@@ -2632,33 +2632,7 @@ internal void ForgetFile(File file)
     /// <summary>
     /// Used space of the Filesystem in bytes
     /// </summary>
-    public override long UsedSpace
-    {
-        get
-        {
-            long usedCluster = 0;
-            var bitmap = _context.ClusterBitmap.Bitmap;
-            var processed = 0L;
-
-            var bufferSize = (int)Math.Min(4 * Sizes.OneMiB, bitmap.Size);
-            var buffer = ArrayPool<byte>.Shared.Rent(bufferSize);
-            try
-            {
-                while (processed < bitmap.Size)
-                {
-                    var count = bitmap.GetBytes(processed, buffer, 0, bufferSize);
-                    usedCluster += BitCounter.Count(buffer, 0, count);
-                    processed += count;
-                }
-            }
-            finally
-            {
-                ArrayPool<byte>.Shared.Return(buffer);
-            }
-            
-            return usedCluster * ClusterSize;
-        }
-    }
+    public override long UsedSpace => _context.ClusterBitmap.GetUsedClustersCount() * ClusterSize;
 
     /// <summary>
     /// Available space of the Filesystem in bytes